Assembly is a critical step in the HIV-1 life cycle and generally thought to occur through the controlled polymerization of the gag polyprotein, which is transported to the plasma membrane where the assembly takes place and the virus particles are formed and bud out as spherical immature noninfectious particles. Recent data indicate that gag polyprotein can also accumulate and assemble into viral particles in the late endosomes, often called multivesicular bodies (MVB), especially in macrophages. The virus particles are released when MVB fuses with the plasma membrane.
It has recently been shown that a cellular protein, AP-3, directs the intracellular trafficking of gag to the MVB. Immediately after the budding, the particles undergo a process termed as maturation, which is essential for the virus to become infectious, where the gag polyprotein is sequentially cleaved by the viral protease to matrix (MA), capsid (CA), nucleocapsid (NC) and p6 domains as well as two spacer proteins, SP1 and SP2. This process triggers a dramatic change in morphology of the particles and an electron dense core is formed surrounded by conical capsid. The formation of mature capsid (CA) play critical role in viral infectivity. Mutations in the CA have been shown to have detrimental effects in viral assembly. Therefore, capsid plays important role in viral assembly, which is critical in the HIV-1 life cycle and has been considered as potential target for developing new generations of drugs against HIV-1.
The major obstacle in developing drugs against assembly has been the lack of effective screening system although some new assay methods have been reported recently. Despite this difficulty, there are reports of identifying peptides or small molecule compounds that disrupt HIV-1 assembly. The first breakthrough in identifying small molecule inhibitors (CAP-1 and CAP-2) of capsid was reported by Summers' group (J Mol Biol. 327:1013-1020, 2003). Although the affinity (Kd) of CAP-1 to N-terminal CA (N-CA) was only ˜800 μM, the identification was the initiator to search for potential inhibitors against this target. Another potent small molecule inhibitor, PA-457 which targets gag processing, has been recently reported. These small molecule inhibitors interfere with maturation of HIV-1. The later compound is currently undergoing Phase II clinical trials.
Recently, a small linear peptide (CAI) has been identified by phage display technique, which inhibits HIV-1 assembly in vitro by targeting the C-terminal CA (C-CA) of capsid. Although x-ray crystallographic analysis revealed that CAI forms a helix and binds to a hydrophobic groove formed by helices 1, 2 and 4 of C-CA, its conformation in solution has not been reported. The dissociation constant (Kd) was estimated to be ˜15 μM. CAI was the first compound reported to have inhibition against both immature and mature HIV-1 particles in vitro. However, the major drawback of CAI is that it cannot penetrate cells, thereby, cannot be used as an assembly inhibitor in living cells.
It would be desirable to have an inhibitor of HIV assembly that can penetrate infected cells. The present disclosure addresses that need.